CHANGES IN MAXIMUM VISCOSITY OF WHEAT-FLO UR AND THE RELATIONSHIP TO CLIMATIC CONDITIONS DURING RIPENING

In order to study the relationship between climatic conditions and max imum viscosity (MV) in wheal flour, changes in MV and alpha-amylase ac tivity by calendar day were investigated. Two winter and two spring wh eat cultivars were harvested at 3-day intervals in 1992 and 1993. Spri ng cultivars flowered about two weeks later than winter cultivars, but MV of these cultivars decreased to below 300 B. U. at almost the same day in each year: MV decreased to below 300 B. U. from August 11 to 1 7 in 1992, and from July 21 to 27 in 1993. alpha-Amylase activity incr eased over 10 Abs/g during the same periods. In 1992, about 60 mm prec ipitation was recorded from August 8 to 10, and MV probably decreased due to this precipitation. However, the precipitation from July 18 to 26 in 1993 was 3 mm, and MV probably decreased to below 300 B. U. due to other climatic conditions. During the period when MV decreased in 1 993, there were low temperatures and little sunshine. These conditions probably reduced MV by inhibiting grain desiccation. In 1993, MV was maintained at a high level in precipitation cut-off treatment. This su ggested that a little rain or dew at night, which were not recorded as precipitation, affected MV. The following tendencies were observed wi th the decrease of MV in 1993:the maximum alpha-amylase activity was l ow, MV and alpha-amylase activity depended on cultivars, and other flo ur traits did not worsen. The climatic conditions when MV decreased to below 300 B. U, in 1993, were similar to that in 1988. From the resul ts, it was suggested that the decrease in MV through lack of rainfall is not an exceptional phenomenon in the Tokachi district, and MV may d ecrease with lack of rainfall.